Apparatus and method providing transformation for human touch force measurements

ABSTRACT

An apparatus includes a force sensor configured to be activated by a user and a control unit connected to an output of the force sensor. The control unit is configurable to operate in response to receipt of an m-bit value representing a measurement from the force sensor to transform the m-bit value to an n-bit transformed value, where n&lt;m, and where the transformed value encodes an identification of one of a plurality of force ranges and contains a force measurement value within the identified one of the plurality of force ranges.

TECHNICAL FIELD

The exemplary and non-limiting embodiments of this invention relategenerally to user input systems, methods, devices and computer programproducts and, more specifically, relate to techniques for sensing andrepresenting an amount of force applied to a touch sensitive haptic userinterface input device.

BACKGROUND

As user interfaces evolve there is a growing interest in, and use of,touch sensitive devices that are capable of generating an output signalthat represents an amount of force applied to the device by a user.These types of devices can be contrasted to conventional force-activateduser input devices, such as pushbutton and similar switches, thatessentially simply indicate that the user has applied a sufficientamount of force to activate the switch, and no more.

Representative publications include the following: “Evaluating DifferentTouch-based Interaction Techniques in a Public Information Kiosk”, RoopeRaisamo, Technical Report of University of Tampere, A-1999-11 (1999);“Making an Impression: Force-Controlled Pen Input for Handheld Devices”,Sachi Mizobuchi, Shinya Terasaki, Turo Keski-Jaskari, Jari Nousiainen,Matti Ryynanen, Miika Silfverberg, CHI 2005, Apr. 2-7, 2005, Portland,Oreg., USA; “Pressure Widgets”, Gonzalo Ramos, Matthew Boulos, RavinBalakrishnan, CHI 2004, Apr. 24-29, 2004, Vienna, Austria; “SensingPressure for Authentication”, Neil Henderson, Neil White, RaymondVeldhuis, Pieter Hartel, Kees Slump, Proc. 3rd IEEE Benelux SignalProcessing Symposium (SPS-2002), Leuven, Belgium, Mar. 21-22, 2002; and“Human Performance in Controlling Normal Forces of Contact with RigidObjects”, Mandayam A. Srinivasan, Jyh-shing Chen, DSC-Vol. 49, Advancesin Robotics, Mechatronics and Haptic Interfaces, ASME 1993.

There are several problems inherent in the use of conventional forcesensitive user input devices. These problems relate generally to thefact that a user's force sense is not linear, and furthermore is notuniform across a given population of users.

SUMMARY OF THE EXEMPLARY EMBODIMENTS

The foregoing and other problems are overcome, and other advantages arerealized, in accordance with the non-limiting and exemplary embodimentsof this invention.

In a first aspect thereof the exemplary embodiments of this inventionprovide a method that includes providing an m-bit value representing ameasurement from a force sensor activated by a user of a device, andtransforming the m-bit value to an n-bit transformed value, where n<m,and where the transformed value encodes an identification of one of aplurality of force ranges and contains a force measurement value withinthe identified one of the plurality of force ranges.

In a further aspect thereof the exemplary embodiments of this inventionprovide a computer-readable memory medium storing computer programinstructions the execution of which results in operations that compriseinputting an m-bit value representing a measurement from a force sensoractivated by a user of a device; and transforming the m-bit value to ann-bit transformed value, where n<m, and where the transformed valueencodes an identification of one of a plurality of force ranges andcontains a force measurement value within the identified one of theplurality of force ranges.

In another aspect thereof the exemplary embodiments of this inventionprovide an apparatus that includes a force sensor configured to beactivated by a user and a control unit connected to an output of theforce sensor. The control unit is configurable to operate in response toreceipt of an m-bit value representing a measurement from the forcesensor to transform the m-bit value to an n-bit transformed value, wheren<m, and where the transformed value encodes an identification of one ofa plurality of force ranges and contains a force measurement valuewithin the identified one of the plurality of force ranges.

In another aspect thereof the exemplary embodiments of this inventionprovide an apparatus that includes means for providing an m-bit valuerepresenting a measurement from a force sensor activated by a user, andmeans for transforming the m-bit value to an n-bit transformed value,where n<m, and where the transformed value encodes an identification ofone of a plurality of force ranges and contains a force measurementvalue within the identified one of the plurality of force ranges, wherethe identification is encoded using a most significant bits of thetransformed value, and where the force measurement value is contained inn-a least significant bits of the transformed value.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other aspects of the teachings of this invention aremade more evident in the following Detailed Description, when read inconjunction with the attached Drawing Figures, wherein:

FIG. 1 is a block diagram of a device constructed and operated inaccordance with the exemplary embodiments of this invention.

FIG. 2 is a graph that illustrates the shape of several exemplarycurves, including a measured response curve from a force sensor, and twoembodiments of transformed response curves.

FIG. 3 shows a non-limiting example of the transformation of an m-bitvalue representing a measurement from the force sensor to an n-bittransformed value, where n<m, and where the transformed value encodes anidentification of one of a plurality of force ranges and contains aforce measurement value within the identified one of the plurality offorce ranges.

FIGS. 4, 5 and 6 are each a logic flow diagram descriptive of a method,and the result of execution of computer program code, in accordance withthe exemplary embodiments of this invention.

DETAILED DESCRIPTION

The exemplary embodiments of this invention are concerned with a forcesensor that provides, for example, 12-bit resolution, at least in alinear measurement. However, 12-bit information requires significantlymore processing power than 8-bit information since many data processorstypically operate with bytes (8-bits) and even multiples of bytes.Further, and as was noted above, human force sense is not linear. As aresult, when applying a higher force level the resolution differs fromwhat it would be at a lower force level. As such, a greater amount ofresolution is desirable when measuring low forces. In addition, it hasbeen found that when measuring force levels that some of the output bitsactual indicate noise (force noise) generated by the user. As is knownin the art a typical human subject can controllably apply about onlyabout 10 different force levels. Further, the actual force applied ateach level can differ significantly between subjects. The end result isthat the force measurement input device should ideally operate over awide dynamic range to be usable with a broad and diverse population ofusers.

Reference is made to FIG. 1 for illustrating a simplified block diagramof a non-limiting embodiment of an electronic device 10 that is suitablefor use in practicing the exemplary embodiments of this invention. Thedevice 10 includes a control unit, such as a microcontroller or dataprocessor 12 that is coupled or connected with at least one memory 14.The memory 14 stores a program (PROG) 14A of computer programinstructions for directing the operations of the data processor 12,including operations that implement the exemplary embodiments of thisinvention as described below. The device 10 may also include a forcemeasurement conditioning function or unit 16 that receives an input 18Arepresenting m-bit information from a force sensor 18 disposed on or in,or otherwise is coupled to the device 10. The force measurementconditioning unit 16 transforms the m-bit information to n-bitinformation, where n<m, and provides an output signal 12A to the dataprocessor 12. In an alternate embodiment the force measurementconditioning unit 16 may not be present, and the force sensor 18 mayprovide an output 12A′ directly to the data processor 12. In this latterembodiment the data processor 12 performs the functions of the forcemeasurement conditioning unit 16.

As a non-limiting example, m=12 and n=8.

The force sensor 18 may be embodied in many different forms. As onenon-limiting example the force sensor 18 may be embodied in a touchsensitive display screen that responds to pressure applied by a user'sfinger or by a stylus. In another non-limiting embodiment the forcesensor 18 may be embodied in a stylus having a deflectable or deformabletip portion that generates an output when pressed against a surface. Inanother non-limiting embodiment the force sensor 18 may be embodied witha push button switch or membrane or dome that outputs a signalindicating an amount of force applied by a user's finger, or it may beembodied in a joystick-type device. The force sensor 18 is assumed to bedisposed relative to the device 10 so that a user is able to exert aforce on the force sensor 18. Note that in some embodiments the forcesensor 18 may be tethered to the device 10 through a cable, such as whenthe force sensor 18 is embodied in a force-sensing stylus. In anotherembodiment the force sensor 18 may be wirelessly coupled to the device10 using, for example, a low power RF link (e.g., a Bluetooth™ link) oran infrared (IR) link. All of these possible embodiments are merelyexemplary, and are not intended to be construed in a limiting fashionwith regards to the many possible forms that the force sensor 18 mayassume.

Note that the device 10 may also include at least one wirelessinterface, such as a radio frequency (RF) transceiver 26 that isconnected with RF circuitry 28 and at least one antenna 30. For example,the device 10 may be a cellular phone that includes the force sensor 18as a user input device.

In general, the various embodiments of the device 10 can include, butare not limited to, cellular telephones, personal digital assistants(PDAs), portable computers, image capture devices such as digitalcameras, gaming devices, music storage and playback appliances, Internetappliances, as well as portable units or devices that incorporatecombinations of such functions.

The exemplary embodiments of this invention may be implemented at leastin part by computer software executable by the data processor 12, or byhardware, or by a combination of software and hardware. This appliesalso to the conditioning unit 16, which may be implemented in hardware,or as software executed by the data processor 12, or as a combination ofhardware and software. Note that the operation of the conditioning unit16 may be accomplished at least in part through the use of a look-uptable (LUT), shown for convenience and not as a limitation as the table14B in FIG. 1. In this embodiment the m-bit output of the force sensor18 may be used to address the LUT to retrieve a corresponding n-bitvalue.

The memory 14 may be of any type suitable to the local technicalenvironment and may be implemented using any suitable data storagetechnology, such as semiconductor-based memory devices, flash memory,magnetic memory devices and systems, optical memory devices and systems,fixed memory and removable memory. The data processor 12 may be of anytype suitable to the local technical environment, and may include one ormore of general purpose computers, special purpose computers,microprocessors, digital signal processors (DSPs) and processors basedon a multi-core processor architecture, as non-limiting examples.

The exemplary embodiments of this invention exploit the ability of ahuman subject (a user of the device 10) to distinguish between differentlevels of low force, and the inability of the user to distinguishbetween different levels of higher forces. A low force result may beused in the control of the device 10, while a high force result may beused to prevent the device 10 from being damaged by the excessive use offorce, such as by providing a feedback signal to the user.

The exemplary embodiments of this invention extend user input dynamicsto operate well with touch force recognition systems, and in one aspectthereof address the problem of how best to generate sufficient dynamicinformation from a linear force detector so as to present the dynamicinformation as 8-bit data. An aspect of this invention is thus a coding(and compression) technique for use with the force sensor 18 when itreceives user touch forces. Even more generally, an aspect of thisinvention relates to a technique to transform m-bit data generated bythe force sensor 18 to n-bit data for convenient use by the dataprocessor 12, without sacrificing the user touch dynamic informationrepresented by the m-bit data, particularly at low force levels.

Assuming as a non-limiting example that the linear force measuringdevice embodied in the force sensor 18 generates 12-bit data, then theconditioning unit 16 performs compression/coding to place the outputinto an 8-bit format. A consideration when performing this task is thatwhen generating higher forces the user may generate a higher level offorce noise as well. For example, approximately 20% of the higher forcemay be noise. As such, the output signal 18A from the force sensor 18with a 5 Newton (N) force applied actually contains about a 1N noisecomponent, while a signal representing a 0.5 N applied force containsonly about a 0.1 N noise component. As a result it can be appreciatedthat the measurement resolution need not be as great when measuring ahigh force as when measuring a lower force.

The exemplary embodiments of this invention provide a signaltransformation for human touch force measuring systems. As was noted,human force sense can be very sensitive and accurate at low levels offorce. In fact, human force sense is generally logarithmic as shown intrace A of FIG. 2. Under normal conditions in the high force area thereare few non-meaningful bits available in the measured results.

More specifically, trace A in FIG. 2 shows a non-limiting and exemplarymeasurement of the force sensor 18 response. After activation of thesensor 18 at about 2 N of applied force the output rises rapidly andreaches a maximum value at about 6-8 N (without saturating). As there isno saturation the user may be encouraged to apply excessive force which,if sufficiently great, may damage the force sensor 18. As can beappreciated, the use of the raw output data form the force sensor 18 isless than desirable, and can create problems. As can be noted, in a lowinput force region of particular interest for many fine-controlapplications (from about 2 N to about 3 N) the corresponding forcesensor output values rise very rapidly, resulting in a possible loss ofcontrol-related information.

In accordance with the exemplary embodiments of this invention theconditioning unit 16 transforms the raw output data of the force sensor18 to provide a non-logarithmic curve shape, such as a generally linearshape (trace B in FIG. 2) or, even more preferably, a generallypolynomial-type curve, such as a second order polynomial curve as shownin trace C that may be deemed to be an optimal response curve.

In FIG. 2, which shows the output values in the range of 0-255 (8-bits),the characteristics of the linear curve of trace B are:

y=min(255,(max(x, 2)−2)*25);

while the characteristics of the optimal curve of trace C are:

y=min(255,(max(x, 2)−2)²*2.5).

It is noted that the curves shown in FIG. 2 are not meant to impose anytype of limitation upon the teachings of this invention. For example,the curve A represents an output measured form a certain type of forcesensor with a certain type of electrical connection. In thisnon-limiting example the force sensor used was one commerciallyavailable from Panasonic as a force sensitive joystick based on asemiconductive polymer material having a characteristic electricalresistance that decreases when compressed. The curve of B depicts anoutput of a certain linear type of force measurement sensor, such as onebased on a piezo-electric effect, and is provided to show one possibleresult of the operation of the conditioning unit 16 when receiving agenerally logarithmic measurement result of a type shown in curve A. Theexemplary curve C is also provided to show a non-limiting example of anon-logarithmic curve shape that is one possible result of the operationof the conditioning unit 16 of FIG. 1.

FIG. 3 illustrates a non-limiting embodiment of an algorithm executed bythe conditioning unit 16 for transforming the measured value from theforce sensor 18 (assumed here to be a 12-bit output from ananalog-to-digital converter that may form a part of the force sensor 18)to a corresponding 8-bit value that can be readily processed by the dataprocessor 12. In this example eight modes (eight force ranges) areconsidered (0-7, with mode 0 being a lowest range of forces and mode 7being a highest range of forces). In each mode range the correspondingtransformed 8-bit output has five least significant bits (LSBs, xxxxx)obtained directly from the measured output value. In the two lowestforce mode ranges these five LSBs are obtained directly from the fiveLSBs of the measured output value, while in the higher force range modesthe five LSBs are obtained directly from five intermediate bits of themeasured output values. Those bits marked as “y” in the measured outputvalue are not used (discarded) in the 8-bit representation. Discardingthese bits in the higher forces range modes effectively filters forcenoise from the transformed 8-bit value, with higher force range modesexperiencing greater filtering than lower force range modes (except forthe two lowest force ranges, where no filtering is performed). The threemost significant bits (MSBs) of the transformed 8-bit value directlyencode the identification of the applicable mode of the eight possiblemodes (000-111). The eight modes are distinguished by a change of stateof a next most significant bit after those five bits (xxxxx) in themeasured output value that are directly represented in the corresponding8-bit output value. As can be appreciated, any given one of the 8-bitvalues directly encodes one of a plurality of applicable force ranges(modes), and also contains one of 32 (represented by 5-bits) forcemeasurement values within that range. Of course, in another embodimentone could encode more or less that eight force ranges (modes), with acorresponding possible change in the number of discrete values that arerepresentable for each range. That is, and by example, in anotherembodiment one may encode 16 different force ranges (modes) using thefour MSBs of the 8-bit value, and represent one of 16 (represented bythe four LSBs) force measurement values within each of the 16 ranges.

As should also be appreciated, the transformation technique of FIG. 3can be readily implemented by use of the look-up table (LUT) procedure,where all (or at least a portion of) the m-bit measured value is used toaddress the LUT to obtain a corresponding n-bit transformed output.

The exemplary embodiments of this invention thus provide a method thatincludes, as shown in FIG. 4, at Block 4A providing an m-bit valuerepresenting a measurement from a force sensor activated by a user of adevice, and at Block 4B transforming the m-bit value to an n-bittransformed value, where n<m, and where the transformed value encodes anidentification of one of a plurality of force ranges and contains aforce measurement value within the identified one of the plurality offorce ranges.

The exemplary embodiments of this invention also provide a method (andcorresponding apparatus and computer program) that includes, as shown inFIG. 5, at Block 5A providing a value representing a measurement from aforce sensor activated by a user of a device; and (Block 5B)transforming the value to a transformed value, where the transformedvalue encodes an identification of one of a plurality of force rangesand contains a force measurement value within the identified one of theplurality of force ranges, and where transforming removes noise from thetransformed value.

The method, apparatus and computer program as in the precedingparagraph, where more noise is removed from a transformed value in ahigher force range than from a transformed value in a lower force range.

The exemplary embodiments of this invention also provide a method (andcorresponding apparatus and computer program) that includes, as shown inFIG. 6, at Block 6A providing a value representing a measurement from aforce sensor activated by a user of a device; and (Block 6B)transforming the value to a transformed value, where the transformedvalue encodes an identification of one of a plurality of force rangesand contains a force measurement value within the identified one of theplurality of force ranges, and where transforming changes a measurementof input force having a substantially logarithmic curve shape into asubstantially non-logarithmic curve shape.

The various blocks shown in FIGS. 4, 5 and 6 may be viewed as methodsteps, and/or as operations that result from operation of computerprogram code, and/or as a plurality of coupled logic circuit elementsconstructed to carry out the associated function(s).

In general, the various exemplary embodiments may be implemented inhardware or special purpose circuits, software, logic or any combinationthereof. For example, some aspects may be implemented in hardware, whileother aspects may be implemented in firmware or software which may beexecuted by a controller, microprocessor or other computing device,although the invention is not limited thereto. While various aspects ofthe exemplary embodiments of this invention may be illustrated anddescribed as block diagrams, flow charts, or using some other pictorialrepresentation, it is well understood that these blocks, apparatus,systems, techniques or methods described herein may be implemented in,as non-limiting examples, hardware, software, firmware, special purposecircuits or logic, general purpose hardware or controller or othercomputing devices, or some combination thereof.

As such, it should be appreciated that at least some aspects of theexemplary embodiments of the inventions may be practiced in variouscomponents such as integrated circuit chips and modules. The design ofintegrated circuits is by and large a highly automated process. Complexand powerful software tools are available for converting a logic leveldesign into a semiconductor circuit design ready to be fabricated on asemiconductor substrate. Such software tools can automatically routeconductors and locate components on a semiconductor substrate using wellestablished rules of design, as well as libraries of pre-stored designmodules. Once the design for a semiconductor circuit has been completed,the resultant design, in a standardized electronic format (e.g., Opus,GDSII, or the like) may be transmitted to a semiconductor fabricationfacility for fabrication as one or more integrated circuit devices.

Various modifications and adaptations may become apparent to thoseskilled in the relevant arts in view of the foregoing description, whenread in conjunction with the accompanying drawings and the appendedclaims. As but some examples, the use of other similar or equivalentforce sensors may be employed.

Further, it should be noted that it is within the scope of thisinvention to integrate the functionality of the conditioning unit 16,the LUT (if used) and so forth into the force sensor apparatus itself,and to thereby directly output the transformed n-bit signal as describedabove.

Note further that the references above to m-bit and n-bit signals shouldnot be construed as implying that parallel data transfer buses need beused, as these signals could be conveyed through serial links as well.

All such and similar modifications of the teachings of this inventionwill still fall within the scope of this invention.

It should be noted that the terms “connected,” “coupled,” or any variantthereof, mean any connection or coupling, either direct or indirect,between two or more elements, and may encompass the presence of one ormore intermediate elements between two elements that are “connected” or“coupled” together. The coupling or connection between the elements canbe physical, logical, or a combination thereof. As employed herein twoelements may be considered to be “connected” or “coupled” together bythe use of one or more wires, cables and/or printed electricalconnections, as well as by the use of electromagnetic energy, such aselectromagnetic energy having wavelengths in the radio frequency region,the microwave region and the optical (both visible and invisible)region, as several non-limiting and non-exhaustive examples.

Furthermore, some of the features of the examples of this invention maybe used to advantage without the corresponding use of other features. Assuch, the foregoing description should be considered as merelyillustrative of the principles, teachings, examples and exemplaryembodiments of this invention, and not in limitation thereof.

1. A method, comprising: providing an m-bit value representing ameasurement from a force sensor activated by a user of a device; andtransforming the m-bit value to an n-bit transformed value, where n<m,and where the transformed value encodes an identification of one of aplurality of force ranges and contains a force measurement value withinthe identified one of the plurality of force ranges.
 2. The method ofclaim 1, where the identification is encoded using a bits, and where theforce measurement value is contained in n-a bits.
 3. The method of claim1, where the identification is encoded using a most significant bits ofthe transformed value, and where the force measurement value iscontained in n-a least significant bits of the transformed value.
 4. Themethod of claim 2, where in at least one force range corresponding to aleast amount of force the n-a bits represent n-a least significant bitsof the m-bit value, and in at least one force range corresponding to agreater amount of force the n-a bits represent n-a bits of the m-bitvalue that are intermediate to a least significant bit and to a mostsignificant bit of the m-bit value.
 5. The method of claim 4, where fora plurality of force ranges corresponding to increasing amounts of forcea number of bits that are intermediate to the n-a bits of the m-bitvalue and the least significant bit of the m-bit value increases,resulting in one or more least significant bits of the m-bit value notbeing represented in the n-bit value.
 6. The method of claim 1, wheretransforming further comprises removing noise from the transformedvalue.
 7. The method of claim 1, where n=8.
 8. The method of claim 1,where transforming results in changing a substantially logarithmic inputforce curve to a non-logarithmic force curve.
 9. The method of claim 1,where transforming results in changing a substantially logarithmic inputforce curve to one of a substantially linear or a substantiallyquadratic force curve.
 10. A computer-readable memory medium storingcomputer program instructions the execution of which results inoperations that comprise: inputting an m-bit value representing ameasurement from a force sensor activated by a user of a device; andtransforming the m-bit value to an n-bit transformed value, where n<m,and where the transformed value encodes an identification of one of aplurality of force ranges and contains a force measurement value withinthe identified one of the plurality of force ranges.
 11. The memorymedium of claim 10, where the identification is encoded using a bits,and where the force measurement value is contained in n-a bits.
 12. Thememory medium of claim 10, where the identification is encoded using amost significant bits of the transformed value, and where the forcemeasurement value is contained in n-a least significant bits of thetransformed value.
 13. The memory medium of claim 11, where in at leastone force range corresponding to a least amount of force the n-a bitsrepresent n-a least significant bits of the m-bit value, and in at leastone force range corresponding to a greater amount of force the n-a bitsrepresent n-a bits of the m-bit value that are intermediate to a leastsignificant bit and to a most significant bit of the m-bit value. 14.The memory medium of claim 13, where for a plurality of force rangescorresponding to increasing amounts of force a number of bits that areintermediate to the n-a bits of the m-bit value and the leastsignificant bit of the m-bit value increases, resulting in one or moreleast significant bits of the m-bit value not being represented in then-bit value.
 15. The memory medium of claim 10, where the transformingoperation further comprises removing noise from the transformed value.16. The memory medium of claim 10, where n=8.
 17. The memory medium ofclaim 10, where the transforming operation results in changing asubstantially logarithmic input force curve to a non-logarithmic forcecurve.
 18. An apparatus, comprising: a force sensor configured to beactivated by a user; and a control unit connected to an output of theforce sensor, said control unit configurable to operate in response toreceipt of an m-bit value representing a measurement from the forcesensor to transform the m-bit value to an n-bit transformed value, wheren<m, and where the transformed value encodes an identification of one ofa plurality of force ranges and contains a force measurement valuewithin the identified one of the plurality of force ranges.
 19. Theapparatus of claim 18, where the identification is encoded using a mostsignificant bits of the transformed value, and where the forcemeasurement value is contained in n-a least significant bits of thetransformed value, where in at least one force range corresponding to aleast amount of force the n-a bits represent n-a least significant bitsof the m-bit value, and in at least one force range corresponding to agreater amount of force the n-a bits represent n-a bits of the m-bitvalue that are intermediate to a least significant bit and to a mostsignificant bit of the m-bit value.
 20. The apparatus of claim 19, wherefor a plurality of force ranges corresponding to increasing amounts offorce a number of bits that are intermediate to the n-a bits of them-bit value and the least significant bit of the m-bit value increases,resulting in one or more least significant bits of the m-bit value notbeing represented in the n-bit value.
 21. The apparatus of claim 18,where said control unit, when transforming the m-bit value, removesnoise from the transformed value.
 22. The apparatus of claim 18, wheren=8.
 23. The apparatus of claim 18, where said control unit, whentransforming the m-bit value, changes a substantially logarithmic inputforce curve to a non-logarithmic force curve.
 24. An apparatus,comprising: means for providing an m-bit value representing ameasurement from a force sensor activated by a user; and means fortransforming the m-bit value to an n-bit transformed value, where n<m,and where the transformed value encodes an identification of one of aplurality of force ranges and contains a force measurement value withinthe identified one of the plurality of force ranges, where theidentification is encoded using a most significant bits of thetransformed value, and where the force measurement value is contained inn-a least significant bits of the transformed value.
 25. The apparatusof claim 24, where in at least one force range corresponding to a leastamount of force the n-a bits represent n-a least significant bits of them-bit value, and in at least one force range corresponding to a greateramount of force the n-a bits represent n-a bits of the m-bit value thatare intermediate to a least significant bit and to a most significantbit of the m-bit value, and where for a plurality of force rangescorresponding to increasing amounts of force a number of bits that areintermediate to the n-a bits of the m-bit value and the leastsignificant bit of the m-bit value increases, resulting in one or moreleast significant bits of the m-bit value not being represented in then-bit value and thereby effectively filtering noise from the transformedvalue.